Electrolytic condenser



Patented M... 22.11934 V 1 ,959,415

UNITED STATES PATENT; OFFICE ELECTROLYTIC CONDENSER Edgar W. Engle, Lake Forest, and Howard L. Cobb,

. Waukegan, 111., assignors to Fansteel Products Company, Inc., North Chicago, Ill., a corporation of New York Application March 16, 1928, Serial No. 262,107

-7 Clgrns. (Cl. 175-315) This invention pertains to electrolytic con- Pa a e indicated y likeareference c ar cdensers and relates more specifically to a uni-diters, rectional condenser in which the filmed electrode F ur 1 is a v t al s ti n of u m v d is immersed in a substantially non-aqueous liquid electrolytic condenser:

I electrolyte Figure 2 is a top plan view of a modification in The object of our invention is to provide an which three filmed electrodes are inserted in a electrolytic condenser which will have a high casingle case; pacity per unit volume and a low electrical leak- Figure 3 is a ve t al c ak elons n s age. 33.0f Figure 2;

A further object. is to provide an electrolytic Figure 4 is a horizontalsection taken at 4-4 of condenser which maintains its film during periods F u e 3; and of idleness and which therefore does not require Figure 51s a detail illustrating the filmed elecreforming to the extent that ordinary aqueous sotrode used in the modification 01' Fi ures 2 t0 4. lution condensers require in As above stated, the condenser comprises a cas- A further object is to provide a junction bein 0 which s preferably of drawn t e a d 79 tween the filmed electrode and its support which which is plated on its exterior surface with cad-' will avoid electrical or chemical action and premium to prevent rusting. It is obvious, however.

vent electrical leakage. that any suitable conductormay be used instead A further object is to provide an improved of drawn steel. v method of forming the film on the electrodes. The case contains an electrolyte 11 which is 75 A further object is to provide a novel structure prepared by heating substantially dry C. P. glycand method of assembling the same which is erin (specific gravity not less than 1.252 at 20 characterized by its simplicity. C.) to a temperature of about 80 C. and stirring A further object is to reduce the cost of manutherein il by weight of sodium bicarbonate facture and assembly of electrical condensers to N8HCO3. About twenty minutes is usually sufa minimum. ficient for completing solution and the glycerin Other objects will be apparent as the detailed is then allowed to cool to room temperature. We description of our invention proceeds. may, of course, use difi'erent amounts of glycerin Our invention my be briefly characterized as and sodium bicarbonate and/or we may use other 30 follows; acids, bases or salts instead of sodium bicarbonate A drawn steel case encloses a filmed electrode without departing from the spirit of our inven- I comprising'cup-shaped aluminum discs spaced tion, the above description being merely of an by aluminum washers secured on an aluminum embodiment which we find at this time gives'the rod which is carried by an inert cover, the edges best results. 35 of which are crimped by the top of the casing to The filmed electrode 12 is held spaced from the 0 form a liquid-tight assembly. The electrolyte is case by a suitable cover 13 of any suitable insu-J a substantially dry (non-aqueous) solution of later which is non-absorbent and chemicaly in glycerin and sodium bicarbonate. A sleeve exert. Phenolic condensation products are espetension or stem surrounds the electrode support cially suitable for this p I 0 and extends below the level of the electrolyte, The filmed electrode is comprised-of a plu- 95 being spaced from the filmed electrode by a mica rality of stamped aluminum discs 14 which are I washer which effectively prevents electrochemical substantially conical or cup-shaped as shown in action to initiate chemical decomposition or leak- Figure 1 with their sides extending v upwardly age in the cell. This washer also prevents the to allow the escape of air bubbleswhich may electrolytic solution from.leaking through the be entrapped. These stamped aluminum discs stem, v are spaced by suitable washers 15, the alternate The invention will be better understood by rediscs and washers being arranged'on an alumiferring to the accompanying drawing and the num rod-16and held in place by a disc 17 which following detailed description in which we speis secured on the rod by spinning or overturncifically define a preferred embodiment of the ining its end as at 18. The upper disc bears against venti n. It 8 to b d tood. h WeV hat a collar 19 on the aluminum rod, which collar the iollowing description is illustrative only and is preferably turned on the rod and is integral that we are not limited to the details given extherewith, A loose .washer or ring may b u d c n as fin d by the appended claims. instead of the integral collar, however, if de- 11 56 In the accompanying drawing, in which simisired.

' The coveror electrode support 13 has an extension or stem 22 in the shape of a sleeve surrounding the upper portion of rod 16. In order to prevent chemical orelectrolytic action from 5 taking place where the aluminum comes in contact with the cover beneath the surface of the electrolyte (as at we provide a mica washer 21. This apparently simple expedient is of utmost importance in the successful operation of the aluminum electrode is in contact with a phenolic condensation product at 20 a chemical change appears to be induced in the condensation product so that its surface'is carbonized and rendered conductive. This, in' turn, causes leakage at 20. The leakage causes sparking, which I still further destroys the film at the point of arcing and finally rendersthe whole condenser inoperative. Our experience has. shown us that unless a washer such as mica, celluloid or other inert insulating material separates the filmed surface from the phenolic condensation product the condensers will inevitably fail at this point when the condensers are subjected to high volt- .ages. The importance of having the sleeve extend below the surface of the electrolyte is well known in the art-that is. it prevents surface 'action due to the combined effect of the air, the

sparking, the electrolyte and the electrolytic gasesjatthis point. f

The upper part of the casing 10 has an annular depression 24 therein giving a circular seat 25 for holding the outwardly extending annular flange 26 on the support or cover 13. This cover is centered by up-standin'g walls 27 and when the cover is placed in position and a suitable gas- 1 lret 28 is placed thereon the upper portion of the walls 2'! are crimped against the'gasket as at 29 to securely hold the parts together and conceal the gasket, the inner portion of the wall 29 preferably just meeting the vertical wall 30 of the; top 13. The gasket 28 is preferably asbestos to which has been added about 10% rubber, although any suitable inert insulating material may be used for this purpose. d

-" The upper surfaceofthe top is provided with I a plurality of ridges 31, 31',between which there is a plurality of annular recesses 32, 32'. The

purpose of this peculiar construction is to cut down surface conduction and 'to prevent shortcircuiting of the condenser by the electrolyte creeping across thetop ofthe condenser-i. e.,

. should the joints around the mica disc 21 or the gasket 28 allow liquid to pass, this liquid will ac- ,cumulate in the grooves 32, 32' before it can creep from the casing 29 to the aluminum rod 16, thus avoiding electrical leakage.

The cover preferably has a small hole 33 drilled rod, preferably by spinning'the' rod "over the lug r This lug is preferably of aluminum to .prevent electrolytic action at sis-shown in Figure 1.

this junction should any electrolyte escape. If dissimilar metals were joined at this point a galvanic couple would result and would cause corrosion if any electrolyte escapes. To facilitate the. soldering of connecting wires we secure our condenser at thehigher voltages because ifa brass-tinned eyelet 3'7 in the aperture 38 the outer end of terminal lug 34.

In Figures 2 to 4-we have shown trodes are inserted in a single cell in place of filmed electrode 12 or Figure 1. These electrodes are aluminum rods 18' which have been turned on a lathe to give a shoulder 19' and a pluraLty of integral spaced discs 14', as shown in Figure 5. By means of a suitable tool this electrode may be turned on a lathe or automatic screw machine by a simple operation and its cost is thereby reduced to a minimum. The cover 13' of this modification has three depending sleeves or stems 22', each surrounding its respective aluminum rod and spaced therefrom by mica washers 21. The method of assembling the gasket 29' and the terminal lug 34', etc., are analogous to the embodiment shown in Figure 1 and further description is unnecessary.

The filmed electrode comprising the punched discs and spacers alternately arranged on the 1 rod as shown in Figure 1 or the turned aluminum rod as shown in Figure 5 are first subjected to a cleaning operation by treatment with alkaline solution followed by a treatment in an acid solution. The electrodes are immersed in a 5% solution of sodium carbonate heated to approximately C. Duringthis immersion the electrodes are 1'05 moved back and forth to replace the air between the plates and to allow the sodium carbonate solution to act readily on all the disc surfaces. In a few seconds all grease particles will be removed and the surfaces of the aluminum will show a slight etched or frosted appearance, a frothy evolution of gas taking. place. The operation is preferably carried out in iron tanksor kettles and the treatment should require ten or fifteen seconds. In practice this step may be dispensed with as the acid cleaning is ordinarily sufilcient to remove all impurities, and to prepare the surface for efficient film forming.

The electrodes are then removed from the soda 120' lng one part by volume of concentrated nitric solution and rinsed in clean water.

The final cleaning solution is prepared by mixacid with three parts of water although other acid concentrations may be used if desired. The

125 ration is t The electrodes are next thoroughly rinsed in clean water, followed by rinsing in distilled water,

it being absolutely essential that all traces of acid v 1 a be removed before further proceeding. The acid is preferably removed by blowing out the remain;

ing water with a jet of compressed air. The plates" at this stage of the process shouldbe of a unian embcdi-"-- ment of our invention wherein three smaller elee form silvery gray color although too long an] immersion will cause them; to appear non-uniform.

After the disc assembly is cleaned the top 18 and the aluminum lug 34 is spun to the other end of the rod 16, care being taken to prevent dirt or impurities of any kind from contaminating the assembly.

The next operati n is the A. C. forming which is carried out with tal immersion of the plates by means of a suitable clamp in a solution of 2% C. P. sodium bicarbonate in distilled water. The

concentration of this solution may be varied depending upon the forming voltage, the more dim 1,050,415 lute solutions being used for higher voltages. an

.products away from the plates and out of the bath. Thisbathispreferablyinasteeltankand the plates are immersed therein in two groups,

each group being a pole from the A. C. supply.

Thediscassemblyispreferablyimmersedinthe solution so that the surface of the electrolyte comes approximately W above the top disc.

give about one-half ampere per large disc assembly (about 38 discs one inch in diameter) and a corresponding current'for electrodes of other areas. The initialpotential is about 50 volts and this potential is gradually raised during about five minutes to a value of 290 volts during which interval the current falls to a substantially constant value. The proper rate of forming can be governed by suitable resistance or reactance in series with the current supply as is well known in this art. Preferably the 290 volts is reached in about four minutes and held at this voltage until the current is constant, which probably takes one or two minutes longer. The

, initial forming with A. C. is important in that it builds up a more rugged film and one less likely to have imperfections or points of weakness. v

The groups of A. C. formed plates are next given a D. C. forming which is preferably accomplished by using the steel container as-a negative pole and all of the aluminum plates as a positive pole. Thisiorming is carried onin the same tank without disturbing the plates by switching from the A. C. supply to a D. C. supply. The D. C. process requires from two and one-hall to three hours in the 2% aqueous solution of sodium carbonate. The temperature should be kept below 40' C. as streaking of the plates is liable to occur at higher temperatures.

Instead of completing the A. C. forming before the D. C. is initiated we may alternate these treatments. progressively increasingthe' voltage on the A. C. and D. C. on each application and keeping the current substantially constant until the voltage has reached a maximum, then allowing the current to drop to a minimum. By this alternate treatment a very rugged and resistant film is built-upon the aluminum electrode.

The electrodes are then carefully removed from the forming tank and are dried bya compressed air Jet which thoroughly removes the forming solution. In' this operation and in all subsequent operations it isextremely essential that the electrode assemblies be handled with'the least possible amount of mechanical abrasion. A break in the film will either make' the condenser nonusable or greatly lengthen the time of the necessary final forming operation.

- The final forming operation is in a substantially dry solution prepared by dissolving 3 5% of sodium bicarbonate in glycerin. It will probably be necessary to heat the glycerin slightly in order to effect solution, a temperature of C. for about twenty minutes usually being required. Care should be taken to keep the glycerin from the top surface of the cover 13 as it is very hard to removea'nd may cause a leakage and ruin the condenser. The dried electrodes are immersed in this glycerin-sodium bicarbonate solution and al-' .cluding a sleeve of a phenolic condensation prodtion between these elements.

D. C. potential is then applied and the electrodes are subjected to 250 volts until the leakage reaches the desired minimum. F

The formed electrodes are then carefully'ralsed from this bath without removing the electrolyte held by the discs and are slipped intothe casing 10 which is previously filled with the same glycerin solution to such a level that the final electrolyte level will be about inch above the top plate of the assembly. Special care must be taken in this step to prevent the electrode from touching the side oi the casing or any other object. The input A. C. current supply is regulated to After the disc assemblies have been inserted in the'casing 10 the gasket 28 is inserted and thetops are sealed by crimping the top edge 29 of the container over the gasket. The assembled condensers are then connected to a 250 volt D. C.

supply and should show a leakage of less than one mil per assembly. The 250 volt potential isv maintained until the current drops to less'than of a mil. Defective condensers can be detected by their high leakage.

The final condenser prepared as above de scribed is about 2 high and 1 in diameter, has a capacity of 10 microfarads, hasa leakage of less than miliamps at 250 voltsD. C., is substantially stable-that is, does not require retrolyte of sodium bicarbonate in glycerin, it is understood that any suitable filmed electrode, such as tantalum, etc., could-be used instead of aluminum. also other alcohols, especially polyhydric alcohols such as ethylene glycol, etc., can

be used instead of glycerin, any ionogen may be substituted for the sodium bicarbonate andgelatin or other material may be added to the electmlyte without departing from the spirit of our 'invention. v a

We claim:

1. In an electrolytic condenser of the filmed electrode fiuid electrolyte type,.non-absorbent, 12o phenolic insulating means for preventing corrosion at the point where the electrode enters the solution including a sleeve around a portion of the electrode and extending below the surface of the fiuid and an inert insulator interposed between said sleeve anda portion of the electrode which is exposed to the electrolyte.

2. A condenser comprising a filmed alumln electrode, a fiuld electrolyte, a sleeve oi a phenolic condensation product surrounding a portion of said electrode and extending below the surface of-the electrolyte, and an inert spacer at the-end of said condensation product and beneath the surface of said electrolyte, separating said condensation product from said filmed electrode.

' 3. In an electrolytic condenser comprising an' aluminum electrode in a fiuid electrolyte, means for preventing surface action and leakage in uct surrounding said electrode and extending below the surface of the electrolyte and a mica washer spaced between said sleeve and said elec-v trode to form a seal and to prevent chemical ac- 4. 'A filmed electrode for electrolytic condensers comprising an aluminum rod provided with a collar intermediate its ends, and having both of its ends overturned, discs retained between the collar and one overturned end and a support and protective sleeve retainedbetween the collar and the otheroverturned end. '5. An electrolytic condenser comprising in combination a metal casing serving as an electrodm a;non-conductive cover for said casing, a rod supported by said cover, a plurality of spaced aluminum discs onsaid rod, and aluminum spacers' maintaining said discs in intimately disposed spaced relation on said rod, said rod, discs and spacers constituting a filmed electrode having an 1 unbroken electrolytic film.

'6. Anelectrolytic condenser comprising an electrolyte, a filmed electrode submerged therein, a phenolic condensation product support for said whereby chemical and electrolytic action therebetween is prevented;

EDGAR W. ENGLE. 'HOWARD L. COBB. 

